Triimide-Functionalized n-Type Polymer Semiconductors Enabling All-Polymer Solar Cells with Power Conversion Efficiencies Approaching 9%

Two triimide-functionalized n-type acceptor polymers are designed and synthesized, which show narrower bandgap, lower-lying frontier molecular orbital energy levels, and improved film morphology than the diimide-functionalized analogue polymers. When blended with a p-type donor polymer semiconductor PTB7-Th, an outstanding power conversion efficiency of 8.98% with a remarkable open-circuit voltage of 1.03 V is attained. This efficiency is among the highest values in all-polymer solar cells (all-PSCs) reported till today, surpassing that (6.85%) of the diimide-functionalized analogue polymers by a big margin and even higher than that (8.69%) of the fullerene-based solar cells. The results demonstrate that the triimide-functionalized f-BTI3 is an excellent building block for developing n-type polymer semiconductors, and the polymer f-BTI3-T is among the best-performing n-type polymers for applications in all-PSCs. The structure–property correlations of these imide-functionalized polymer semiconductors offer important guides for developing high-performance n-type polymer semiconductors.